1. Technical Field
The present invention relates to an energy absorbing device for a collapsible steering column in which the resistance to collapsing can be varied.
2. Description of the Prior Art
U.S. Pat. No. 4,886,295 describes a vehicle occupant protection system including a collapsible steering column. An energy absorber is located between two relatively movable sections of the steering column. The energy absorber includes an inflatable bag. The vehicle has electric circuitry, including sensors for sensing vehicle and occupant conditions, that controls the state of inflation of the inflatable bag to vary the energy absorbing capacity of the steering column.
It is known to use electrorheological fluid in an energy absorber for an engine mount or another structure having two relatively movable parts. Typical structures incorporating such a fluid are disclosed in U.S. Pat. Nos. 5,176,368 and 5,655,757. Varying the strength of an energy field acting on the fluid can vary the apparent viscosity of the fluid, thus controlling the energy absorption characteristics of the device.